The independent and interdependent effects of vagal afferent impulses on the regulation of the respiratory system, especially on mechanisms which establish the frequency and volume of a respiratory cycle is being studied. The transient and steady-state responses to vagal blockade produced by cooling a short segment of one nerve, while the contralateral nerve is cut, during normoxia, hypoxia and hypercapnia are being investigated. Similar experiments will be performed with the carotid chemoreceptors intact and following chemoreceptor denervation. The effects of interaction of vagal afferent impulses with carotid sinus baroreceptor afferent impulses will be studied by creating conditions of hypotension and hypertension. Current studies indicate that under normoxic, normocapnic conditions the tidal volume reaches a new steady state immediately after vagal cooling while other parameters of the respiratory cycle require ten or more minutes to reach a new steady state. The effects of hypoxia and hypercapnia on time to reach a new steady state is under investigation. The effects of vagal impulses at various times in the respiratory cycle is being studied by electrically blocking afferent nerve conduction. This technique, shown to produce immediate and complete block of the nerve, reveals the effects of sudden withdrawal of feed-back information from the lungs on the characteristics of the phase of the cycle in which it is applied and on subsequent phases of the cycle. It was found that application to electrical block during various times after inspiration has begun results in the same proportionate increase in volume that occurs when the block is applied before inspiration starts. The effects of hypoxia and hypercapnia on this response also will be studied.